1. Field of the Invention
The present invention relates to a pointing device for a computer, and more specifically to a pointing device for a computer that makes use of a magnetic field source and magnetic field sensors.
2. Description of the Prior Art
Pointing devices such as computer mice are one of the most popular methods of user interaction with a computer. A mouse can be used to position a cursor on a computer screen and to execute commands. There are several popular prior art mouse designs currently available to consumers.
A common prior art mouse design is shown in FIG. 1. A mouse 10 comprises a body 12, buttons 14 disposed on the body 12, and a connector cable 16 attached to the body 12. The connector cable 16 can electronically connect the mouse 10 to a computer. To interact with the computer, a user can move the body 12 across a flat surface and depress the buttons 14.
A cross-sectional view of the mouse 10 is shown in FIG. 2. Disposed inside the mouse 10 is a weighted ball 18 that is able to roll when the mouse 10 is moved across a flat surface, a roller 19 having an attached slotted disk 20, the roller 19 in contact with the weighted ball 18, and a pair of infrared sensors 22 (only one is shown in FIG. 2) that can sense the rotation speed of the slotted disk 20 in a direction parallel to an arrow 28. Normally, a second roller and attached slotted disk and a second pair of infrared sensors are provided to sense the rotation speed of the weighted ball 18 in a second direction perpendicular to the arrow 28 and the plane of FIG. 2, but for clarity, these are not shown in FIG. 2. The infrared sensors 22 are electrically connected to a circuit 24, which processes signals received from the infrared sensors 22. Button switches 26 are triggered by the buttons 14 and are electrically connected to the circuit 24. The circuit 24 generates and outputs digital signals relating to the position of the mouse body 12 and the status of the buttons 14 to the computer via the connector cable 16.
FIG. 2 also illustrates the working principle of the mouse 10 in one dimension. When a user slides the body 12 of the mouse 10 across a flat surface parallel to the arrow 28, a frictional force, also indicated by the arrow 28, is exerted on the weighted ball 18 where it contacts the flat surface. The rotation of the ball 18 causes the roller 19 and slotted disk 20 to rotate. The pair of infrared sensors 22 senses the rotation of the roller 19 as pulses caused by the slotted disk 20 and sends a corresponding signal to the circuit 24. If at this time the user presses the buttons 14, the button switches 26 transmit signals to the circuit 24. The circuit 24 then generates and outputs digital signals relating to the position of the mouse body 12 and the status of the buttons 14. The digital signals are output through the connector cable 16 and into the computer. In this way, the prior art mouse 10 can be used to interface with the computer.
The prior art weighted ball style mouse has several deficiencies. Primarily, a weighted ball will simply not roll if the mouse is not in direct contact with a flat surface. Moreover, the flat surface must have a suitable texture in order for the weighted ball to roll reliably. In addition, this variety of mouse is limited to resolving movement in two dimensions only, in the plane of the flat surface. Finally, the roller and sensor mechanism is susceptible to damage by dust particles and intrusion by other particulates.
Another recently popular prior art mouse design is an optical mouse. The optical mouse comprises a light emitting diode (LED) and an image sensor. As the optical mouse is moved over a flat surface, light emitted by the LED is reflected off the flat surface and back to the image sensor. Image data is then analyzed by a processor to correlate patterns and accordingly determine the direction and speed of the movement of the mouse. The processor then sends digital signals to the computer relating the movement and button status of the mouse.
The prior art optical mouse also has faults similar to the weighted ball style mouse, specifically, a flat surface must be provided from which light can reflect. Consequently, this type of mouse is limited to movement in the plane of the flat surface. In addition, dust or other matter can obstruct the LED or image sensor and cause a malfunction.
Both prior art mouse designs described suffer similar inherent limitations. The first being that contact with a flat surface is necessary. The second limitation being that the sensing elements, which are open to the environment, can be impaired by dust or other potentially harmful matter.